An ultrasonic temperature sensor has been disclosed in U.S. Pat. No. 4,541,732 (Shah). The device disclosed in this patent makes accurate and highly sensitive temperature measurements by means of an ultrasonic wave which is caused to traverse a path which has a temperature sensitive modulus. The speed of propagation and hence the traverse time of the wave over the path is a function of temperature so that temperature can be measured by means of a time difference approach. A temperature detector using a surface acoustic wave device is disclosed in U.S. Pat. No. 4,249,418 (Ebata). The disclosed apparatus includes a signal processing circuit for processing the output of the detecting means to generate a temperature display.
In U.S. Pat. No. 4,593,567 (Isselstein et al), an electromagnetic transducer is disclosed for the transmission and reception of ultrasonic waves. The transducer is arranged for the continuous fault testing of a material by wave length spectroscopy and in particular modal spectroscopy. Another electromagnetic acoustic transducer is disclosed in U.S. Pat. No. 4,395,913 (Peterson). This fault detecting transducer utilizes plural wavelengths.
A method and apparatus for measuring stress in a material using periodic permanent magnet electromagnetic acoustic transducers is disclosed in U.S. Pat. No. 4,522,071 (Thompson).